Curable Silicone Composition That Provides A Highly Transparent Cured Silicone Material

ABSTRACT

A curable silicone composition comprises (A) (A-1) a dialkylpolysiloxane that has at least two alkenyl groups in each molecule and a viscosity of at least 1,000 mPa·s to not more than 50,000 mPa·s and (A-2) an alkenyl-containing, resin-form organopolysiloxane that comprises the SiO 4/2  unit, R 1   2 R 2 SiO 1/2  unit, and R 1   3 SiO 1/2  unit wherein R 1  is alkyl and R 2  is alkenyl and that contains the alkenyl group in the range from at least 0.5 mass % to less than 3.5 mass %; (B) an organopolysiloxane that has at least three silicon-bonded hydrogen atoms; and (C) a hydrosilylation reaction catalyst. The curable composition provides a highly transparent cured silicone material that has a hardness in the range from at least 30 to not more than 80, a parallel light transmittance at 25° C. of at least 90%, and a parallel light transmittance at 200° C. that is at least 99% of the parallel light transmittance at 25° C.

TECHNICAL FIELD

The present invention relates to a curable silicone composition thatprovides a flexible and highly transparent cured silicone material. Thepresent invention more particularly relates to a curable siliconecomposition that contains a resin-form organopolysiloxane and thatprovides a flexible and highly transparent cured silicone material thatdoes not undergo temperature-induced changes in its transparency.

BACKGROUND ART

Curable silicone compositions that contain a resin-formorganopolysiloxane and that provide a highly transparent cured siliconematerial are known. For example, JP 2005-042099 (Equivalent to US2005-0006794 A1) A describes a silicone rubber composition comprising anorganopolysiloxane that has at least two aliphatically unsaturated bondsin each molecule; an organopolysiloxane having a resin structure andcomprising the SiO₂ unit, an R₃SiO_(0.5) unit having 2-3 vinyl groups,and an R₃SiO_(0.5) unit having 0-1 vinyl group, wherein the non-vinyl Rin these formulas is monovalent hydrocarbyl that does not contain analiphatically unsaturated bond, e.g., methyl and so forth; anorganohydrogenpolysiloxane that has at least two silicon-bonded hydrogenatoms in each molecule; and a platinum group metal-based catalyst. Inthe following, the SiO₂ unit is referred to as the Q unit and theR₃SiO_(0.5) unit is referred to as the M unit.

The polyorganosiloxane composition described in JP 2006-335857 Aprovides a transparent cured material and comprises a straight-chainpolyorganosiloxane containing silicon-bonded alkenyl and having aviscosity at 23° C. of 10 to 10,000 mm²/s; a branched polyorganosiloxanecomprising the Q unit, an M unit having one vinyl group, and an M unitthat does not contain an aliphatically unsaturated bond; apolyalkylhydrogensiloxane comprising the Q unit, an M unit having onesilicon-bonded hydrogen atom, and an M unit that does not containsilicon-bonded hydrogen; and a platinum group metal compound.

The curable silicone composition described in JP 2007-131694 A(equivalent to US2009-0118441 A1) comprises at least adiorganopolysiloxane that has at least two alkenyl groups in eachmolecule; at least two resin-form organopolysiloxanes that havedifferent mass-average molecular weights, each comprising the Q unit, anM unit having one vinyl group, and an M unit that does not contain analiphatically unsaturated bond; an organopolysiloxane that has at leasttwo silicon-bonded hydrogen atoms in each molecule; and ahydrosilylation reaction catalyst.

JP 2006-328102 A (equivalent to US2006-0264583 A1) describes a siliconepolymer composition for lens molding, that characteristically provides acolorless and transparent cured material and that comprises as itsessential components an organopolysiloxane that has at least twoaliphatically unsaturated bonds in each molecule and a viscosity of atleast 100 mPa·s at 25° C., an organohydrogenpolysiloxane that has atleast three H(CH₃)₂SiO_(1/2) units in each molecule, and a platinumgroup metal catalyst.

However, the cured silicone materials provided by the cure of suchcompositions are prone to breakage during mold-based molding and duringcomponent assembly processes, and it has also not been possible to usethem in applications that demand bendability due to use in a flexed orbent condition. In addition, the cured silicone materials provided bythe cure of these compositions are subject to temperature-inducedchanges in transparency, and problems due to optical property variationsare then produced when these cured silicone materials are used over abroad temperature range.

PATENT REFERENCES

-   Patent Reference 1: JP 2005-042099 A-   Patent Reference 2: JP 2006-335857 A-   Patent Reference 3: JP 2007-131694 A-   Patent Reference 4: JP 2006-328102 A

DISCLOSURE OF INVENTION

An object of the present invention is to provide a curable siliconecomposition that forms a flexible and highly transparent cured siliconematerial that does not undergo temperature-induced changes in itstransparency.

The curable silicone composition of the present inventioncharacteristically comprises

-   (A) 100 mass parts of an alkenyl-containing organopolysiloxane    comprising    -   (A-1) a dialkylpolysiloxane that has an average of at least two        alkenyl groups in each molecule and a viscosity at 25° C. of at        least 1,000 mPa·s to not more than 50,000 mPa·s, at from 50 mass        % to not more than 80 mass % of component (A), and    -   (A-2) an alkenyl-containing, resin-form organopolysiloxane that        comprises the SiO_(4/2) unit, R¹ ₂R²SiO_(1/2) unit, and R¹        ₃SiO_(1/2) unit wherein R¹ is C₁₋₁₀ alkyl and R² is alkenyl and        that contains the alkenyl group in the range from at least 0.5        mass % to less than 3.5 mass %, at from 20 mass % to not more        than 50 mass % of component (A);-   (B) an organopolysiloxane that has an average of at least three    silicon-bonded hydrogen atoms in each molecule wherein the    silicon-bonded groups other than the silicon-bonded hydrogen are    C₁₋₁₀alkyl, in an amount that provides 0.8 to 2 moles silicon-bonded    hydrogen in this component per 1 mole of the total alkenyl in    component (A); and-   (C) a hydrosilylation reaction catalyst in a catalytic quantity,    and provides a highly transparent cured silicone material that    characteristically has a hardness measured using the type A    durometer specified in JIS K 6253 in the range from at least 30 to    not more than 80, an elongation as specified in JIS K 6251 of at    least 50%, a parallel light transmittance at 25° C. measured in    accordance with JIS K 7105 on a 6 mm optical path length of at least    90%, and a parallel light transmittance value at 200° C. that is at    least 99% of the parallel light transmittance at 25° C.

The aforementioned component (B) preferably is an organopolysiloxanecomprising

-   (B-1) an organopolysiloxane that contains at least 0.7 mass %    silicon-bonded hydrogen and that comprises the SiO_(4/2) unit and    HR³ ₂SiO_(1/2) unit wherein R³ is C₁₋₁₀ alkyl, at 50 to 100 mass %    of component (B), and-   (B-2) a straight-chain organopolysiloxane that contains at least 0.3    mass % silicon-bonded hydrogen wherein the silicon-bonded groups    other than the silicon-bonded hydrogen are C₁₋₁₀ alkyl, at 0 to 50    mass % of component (B).

The cured silicone material of the present invention ischaracteristically provided by the thermosetting of the aforementionedcurable silicone composition and has a hardness measured using the typeA durometer specified in JIS K 6253 in the range from at least 30 to notmore than 80, an elongation as specified in JIS K 6251 of at least 50%,a parallel light transmittance at 25° C. measured in accordance with JISK 7105 on a 6 mm optical path length of at least 90%, and a value forthe parallel light transmittance at 200° C. that is at least 99% of theparallel light transmittance at 25° C.

The aforementioned cured silicone material preferably has a hardnessmeasured using the type A durometer specified in JIS K 6253 in the rangefrom at least 65 to not more than 75.

The cured silicone composite according to the present inventioncharacteristically comprises a substrate that forms a single articlewith a cured silicone layer that is provided by the cure of thepreviously described curable silicone composition. This cured siliconecomposite can be obtained by coating the previously described curablesilicone composition on a substrate and then thermosetting the curablesilicone composition.

The curable silicone composition of the present invention, because itcomprises a special alkenyl-functional dialkylpolysiloxane and a specialalkenyl-functional, resin-form organopolysiloxane, characteristicallyprovides a flexible and highly transparent cured silicone material thatcan maintain its high transparency over a broad temperature range fromambient temperature to high temperatures. Because it is flexible, thecured silicone material provided by the cure of this compositioncharacteristically resists breakage during mold-based molding andcomponent assembly processes and thus exhibits an excellent moldabilityand handling characteristics, and can also be used in applications thatdemand bendability, for example, use in a flexed or bent condition. Inaddition, because the present composition does not containsilicon-bonded aryl, for example, phenyl, the cured silicone materialprovided by the cure of the present composition characteristically doesnot suffer from a reduction in transparency even when held under hightemperature, high humidity conditions or when exposed to ultravioletradiation.

BEST MODE FOR CARRYING OUT THE INVENTION

The alkenyl-containing organopolysiloxane that is component (A) is thebase component of the present composition and comprises (A-1) adialkylpolysiloxane that has an average of at least two alkenyl groupsin each molecule and a viscosity at 25° C. of 1,000 mPa·s to 50,000mPa·s, at 50 mass % to 80 mass % of component (A), and (A-2) analkenyl-containing, resin-form organopolysiloxane that comprises theSiO_(4/2) unit, R¹ ₂R²SiO_(1/2) unit, and R¹ ₃SiO_(1/2) unit wherein R¹is C₁₋₁₀ alkyl and R² is alkenyl and that contains the alkenyl group atfrom at least 0.5 mass % to less than 3.5 mass %, at 20 mass % to 50mass % of component (A).

Component (A-1) has an average of at least two alkenyl groups in eachmolecule. Component (A-1) has a substantially straight chain molecularstructure, but a portion of the molecular chain may be somewhatbranched. The alkenyl in component (A-1) can be exemplified by vinyl,allyl, isopropenyl, butenyl, hexenyl, and cyclohexenyl wherein vinyl ispreferred. The bonding position for this alkenyl is not limited and maybe, for example, the terminal position and/or side chain position on themolecular chain wherein terminal position on the molecular chain ispreferred. The alkyl in component (A-1) can be exemplified by C₁₋₁₀alkyl such as methyl, ethyl, propyl, cyclopentyl, cyclohexyl, and soforth, wherein methyl is preferred.

The viscosity of component (A-1) at 25° C. is in the range from 1,000mPa·s to 50,000 mPa·s and preferably is in the range from 1,500 mPa·s to45,000 mPa·s and more preferably is in the range from 2,000 mPa·s to45,000 mPa·s. When component (A-1) is a mixture of two or morealkenyl-functional dialkylpolysiloxanes, the viscosity of this mixtureat 25° C. must be in the range from 1,000 mPa·s to 50,000 mPa·s. As longas the viscosity at 25° C. is in the specified range, component (A-1)may be a mixture of a small amount of an alkenyl-functionaldialkylpolysiloxane gum and an alkenyl-functional dialkylpolysiloxanethat is a liquid at 25° C. The reasons for the preceding are as follows:when the viscosity of component (A-1) at 25° C. is less than the lowerlimit cited above, the cured silicone material provided by the cure ofthe present composition tends to have an unsatisfactory flexibility;when, on the other hand, the viscosity of component (A-1) at 25° C.exceeds the upper limit cited above, the transparency of the curedsilicone material provided by the cure of the present composition tendsto decline at high temperatures, while the present composition assumesan excessively high viscosity and the handling characteristics tend todecline.

This component (A-1) diorganopolysiloxane is exemplified bydimethylpolysiloxanes endblocked at both molecular chain terminals bydimethylvinylsiloxy groups, dimethylsiloxane•methylvinylsiloxanecopolymers endblocked at both molecular chain terminals bydimethylvinylsiloxy groups, methylvinylpolysiloxanes endblocked at bothmolecular chain terminals by trimethylsiloxy groups,dimethylsiloxane•methylvinylsiloxane copolymers endblocked at bothmolecular chain terminals by trimethylsiloxy groups, and mixtures of twoor more of the preceding.

The content of component (A-1) in the present composition is an amountthat is at least 50 mass % to not more than 80 mass % of component (A)and preferably is an amount that is at least 55 mass % to not more than70 mass % of component (A) and particularly preferably is an amount thatexceeds 60 mass % but is not more than 70 mass %. The reasons for thisare as follows: when the component (A-1) content is less than the lowerlimit on the cited range, the flexibility of the cured silicone materialprovided by the cure of the present composition tends to decline; when,on the other hand, the component (A-1) content exceeds the upper limiton the cited range, the hardness of the cured silicone material providedby the cure of the present composition tends to decline.

The alkenyl-containing, resin-form organopolysiloxane that is component(A-2) imparts a satisfactory hardness and flexibility to the curedsilicone material provided by the cure of the present composition andcomprises the SiO_(4/2) unit, R¹ ₂R²SiO_(1/2) unit, and R¹ ₃SiO_(1/2)unit. In these formulas, R¹ is C₁₋₁₀ alkyl such as methyl, ethyl,propyl, cyclopentyl, cyclohexyl, and so forth, and R² is an alkenylgroup such as vinyl, allyl, isopropenyl, butenyl, hexenyl, cyclohexenyl,and so forth, wherein vinyl is preferred.

The component (A-2) alkenyl-containing, resin-form organopolysiloxanecontains the alkenyl group at from at least 0.5 mass % to less than 3.5mass % and preferably contains from at least 1.0 mass % to not more than2.5 mass % alkenyl. The reasons for this are as follows: when thealkenyl content in component (A-2) is less than the cited lower limit,the hardness of the cured silicone material provided by the cure of thepresent composition tends to decline; when, on the other hand, thealkenyl content in component (A-2) exceeds the cited upper limit, theflexibility of the cured silicone material provided by the cure of thepresent composition tends to decline and the transparency of the curedsilicone material provided by the cure of the present composition tendsto decline at high temperatures. Component (A-2) may be a mixture of twoor more alkenyl-containing, resin-form organopolysiloxanes, in whichcase the mixture considered as such must contain alkenyl at from atleast 0.5 mass % to less than 3.5 mass % and preferably contains from atleast 1.0 mass % to not more than 2.5 mass % alkenyl.

The ratio of the total number of moles of R¹ ₂R²SiO_(1/2) and R¹₃SiO_(1/2) units to 1 mole of the SiO_(4/2) unit in component (A-2) ispreferably in the range from 0.50 to 1.80 and particularly preferably isin the range from 0.70 to 1.10. The reasons for this are as follows:when the ratio of the total number of moles of R¹ ₂R²SiO_(1/2) and R¹₃SiO_(1/2) units to 1 mole of the SiO_(4/2) unit in component (A-2) isless than the cited lower limit, component (A-2) takes on an excessivelylarge molecular weight and the transparency of the cured siliconematerial provided by the cure of the present composition may decline;when, on the other hand, the ratio of the total number of moles of R¹₂R²SiO_(1/2) and R¹ ₃SiO_(1/2) units to 1 mole of the SiO_(4/2) unit incomponent (A-2) exceeds the upper limit cited above, the cured siliconematerial provided by the cure of the present composition may have anunsatisfactory strength.

Component (A-2) has a mass-average molecular weight, on a standardpolystyrene basis by gel permeation chromatography, preferably in therange from 3,000 to 7,000 and more preferably in the range from 4,000 to6,000. Component (A-2) may be a mixture of two or morealkenyl-containing, resin-form organopolysiloxanes and is preferably amixture comprising alkenyl-containing, resin-form organopolysiloxanesthat have a mass-average molecular weight, on a standard polystyrenebasis by gel permeation chromatography, in the range from 3,000 to7,000.

The content of component (A-2) in the present composition is an amountthat is at least 20 mass % to not more than 50 mass % of component (A),preferably is an amount that is at least 30 mass % to not more than 45mass % of component (A), and particularly preferably is an amount thatis at least 30 mass % to less than 40 mass % of component (A). Thereasons for this are as follows: when the component (A-2) content isless than the lower limit on the cited range, the hardness of the curedsilicone material provided by the cure of the present composition tendsto decline; when, on the other hand, the component (A-2) content exceedsthe upper limit on the cited range, the flexibility of the curedsilicone material provided by the cure of the present composition tendsto decline and the transparency of the cured silicone material providedby the cure of the present composition tends to decline at hightemperatures.

The organopolysiloxane that is component (B) is a crosslinking agent forthe present composition and contains at least three silicon-bondedhydrogen atoms in each molecule. Viewed from the perspective of thetransparency of the cured silicone material provided by the cure of thepresent composition, the silicon-bonded hydrogen content in component(B) is preferably at least 0.3 mass % and more preferably is at least0.7 mass %. For a hardness of at least 60 for the cured siliconematerial provided by the cure of the present composition, said hardnessbeing measured using the type A durometer specified in JIS K 6253, thesilicon-bonded hydrogen content in component (B) is preferably at least0.7 mass %.

The molecular structure of component (B) can be, for example, straightchain, partially branched straight chain, branched chain, cyclic, ordendritic wherein straight chain, partially branched straight chain, anddendritic are preferred. There are no limitations on the bondingposition of the silicon-bonded hydrogen in component (B), and thesilicon-bonded hydrogen may be bonded in, for example, terminal positionon the molecular chain and/or side chain position on the molecularchain. The silicon-bonded groups in component (B) other than thesilicon-bonded hydrogen are alkyl such as methyl, ethyl, propyl,cyclopentyl, cyclohexyl, and so forth, wherein methyl is preferred. Thisprovides a good compatibility with component (A) and also provides anexcellent transparency for the cured silicone material provided by thecure of the present composition. While there is no limitation on theviscosity of component (B), its viscosity at 25° C. is preferably in therange from 1 to 10,000 mm²/s and particularly preferably is in the rangefrom 1 to 1,000 mm²/s.

An example of a particularly preferred component (B) is anorganopolysiloxane comprising (B-1) an organopolysiloxane that containsat least 0.7 mass % silicon-bonded hydrogen and that comprises theSiO_(4/2) unit and HR³ ₂SiO_(1/2) unit wherein R³ is C₁₋₁₀ alkyl such asmethyl, ethyl, propyl, cyclopentyl, cyclohexyl, and so forth, withmethyl being preferred, at 50 to 100 mass % of component (B), and (B-2)a straight-chain organopolysiloxane that contains at least 0.3 mass %silicon-bonded hydrogen wherein the silicon-bonded groups other than thesilicon-bonded hydrogen are C₁₋₁₀ alkyl, at 0 to 50 mass % of component(B).

In addition to the SiO_(4/2) unit and HR³ ₂SiO_(1/2) unit, component(B-1) may also contain the R³ ₃SiO_(1/2) unit. The ratio of the totalnumber of moles of HR³ ₂SiO_(1/2) and R³ ₃SiO_(1/2) units to 1 mole ofthe SiO_(4/2) unit in component (B-1) is preferably in the range from1.50 to 2.50 and more preferably is in the range from 1.80 to 2.20. Aspecific example of a preferred component (B-1) is theorganopolysiloxane given by (SiO_(4/2))₄(H(CH₃)₂SiO_(1/2))₈.

The component (B-2) straight-chain organopolysiloxane contains at least0.3 mass % and preferably at least 0.7 mass % silicon-bonded hydrogen.The silicon-bonded groups other than the silicon-bonded hydrogen areC₁₋₁₀ alkyl such as methyl, ethyl, propyl, cyclopentyl, cyclohexyl, andso forth, wherein methyl is preferred. Component (B-2) has asubstantially straight chain molecular structure, but a portion of themolecular chain may be somewhat branched. Preferred specific examples ofcomponent (B-2) are dimethylsiloxane•methylhydrogensiloxane copolymersendblocked at both molecular chain terminals by dimethylhydrogensiloxygroups, methylhydrogenpolysiloxanes endblocked at both molecular chainterminals by trimethylsiloxy groups,dimethylsiloxane•methylhydrogensiloxane copolymers endblocked at bothmolecular chain terminals by trimethylsiloxy groups, and mixtures of twoor more of the preceding.

The content of component (B) in the present composition is an amountthat provides from 0.8 to 2 moles and preferably from 0.9 to 1.5 molessilicon-bonded hydrogen atoms in this component per 1 mole of the totalalkenyl in component (A). The reasons for this are as follows: when thecomponent (B) content is less than the lower limit for the cited range,curing of the composition tends to be unsatisfactory; when, on the otherhand, the upper limit for the cited range is exceeded, the flexibilityand/or transparency of the cured silicone material provided by the cureof the present composition may be diminished.

The hydrosilylation reaction catalyst that is component (C) is acatalyst for promoting curing of the present composition and can beexemplified by platinum-type catalysts, rhodium-type catalysts, andpalladium-type catalysts, wherein the platinum-type catalysts areparticularly preferred. These platinum-type catalysts can be exemplifiedby platinum micropowder, platinum black, platinum supported on silicamicropowder, platinum supported on active carbon, chloroplatinic acid,alcohol solutions of chloroplatinic acid, and platinum compounds such asolefin complexes of platinum, alkenylsiloxane complexes of platinum, andso forth.

The component (C) content in the present composition is a catalyticquantity and in specific terms is a quantity that provides 0.01 to 1,000mass-ppm catalyst metal atoms with reference to the present composition.The reasons for this are as follows: when the component (C) content isless than the lower limit for the cited range, the risk arises that thecure of the resulting composition will not proceed adequately; on theother hand, curing is not significantly promoted by exceeding the upperlimit for the cited range, while the risk arises that problems willappear such as discoloration of the cured silicone material.

As other, optional components, the present composition may contain, forexample, a reaction inhibitor in order to adjust the cure rate of thepresent composition, e.g., an alkyne alcohol such as2-methyl-3-butyn-2-ol, 3,5-dimethyl-1-hexyn-3-ol,1-ethynyl-1-cyclohexanol, phenylbutynol, and so forth; ene-yne compoundssuch as 3-methyl-3-penten-1-yne, 3,5-dimethyl-3-hexen-1-yne, and soforth; as well as1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane,1,3,5,7-tetramethyl-1,3,5,7-tetrahexenylcyclotetrasiloxane,benzotriazole, and so forth. There is no limitation on the content ofthis reaction inhibitor in the present composition, and this content maybe selected as appropriate as a function of the molding method andcuring conditions; however, an amount within the range from 10 to 5,000mass-ppm with reference to the present composition is generallypreferred.

The present composition may incorporate, insofar as the object of thepresent invention is not impaired, for example, an adhesion promoter,flame retardant, inorganic filler, and so forth. However, as a generalmatter, an adhesion promoter, flame retardant, and inorganic filler arepreferably not incorporated from the perspective of the transparency ofthe cured silicone material provided by the cure of the presentcomposition.

When the cured silicone material provided by the cure of the presentcomposition is to be used in electrical•electronic applications, thecontent in the present composition of low molecular weightorganopolysiloxane having a molecular weight not more than 650 ispreferably not more than 350 ppm.

The viscosity of the present composition at 25° C. is not particularlylimited, but considered from the standpoint of the moldability andhandling characteristics, i.e., ease of pouring or injection, ease ofdegassing, and so forth, the viscosity of the present composition at 25°C. is preferably 1 to 100 Pa·s and particularly preferably is 2 to 50Pa·s.

The present composition forms a cured silicone material when cured byheating to 100 to 250° C. This cured silicone material according to thepresent invention has a hardness, as measured using the type A durometerspecified in JIS K 6253, in the range from at least 30 to not more than80, preferably in the range from at least 50 to not more than 80, andmore preferably in the range from at least 60 to not more than 75. Thereasons for this are as follows: the cured silicone material may haveinsufficient strength when its hardness is less than the lower limit forthe cited range; when, on the other hand, the upper limit for the citedrange is exceeded, the flexibility of the cured silicone material underconsideration tends to be inadequate. When this cured silicone materialis to be used as an optical member or component, the hardness, asmeasured using the type A durometer specified in JIS K 6253, isparticularly preferably in the range from at least 60 to not more than80 based on a consideration of the moldability and the handlingcharacteristics.

In order to exhibit a satisfactory flexibility, this cured siliconematerial must have an elongation as specified in JIS K 6251 of at least50%. The reason for this is that the flexibility of the cured siliconematerial becomes unsatisfactory at below the indicated range.

The present cured silicone material must have a parallel lighttransmittance at 25° C., measured in accordance with JIS K 7105 on the 6mm-thick cured silicone material, i.e., on a 6 mm optical path length,of at least 90%, and must have a parallel light transmittance at 200° C.that is a value that is at least 99% of the parallel light transmittanceat 25° C. The reason for this is that deficiencies tend to occur inoptical component applications when the present cured silicone materialhas a parallel light transmittance at 200° C. that is less than 99% ofthe parallel light transmittance at 25° C.

In addition, the present cured silicone material may be a composite inwhich the cured silicone material is formed into a single article withany of various substrates. The substrate can be exemplified by variousmetals, thermoplastic plastics, thermosetting plastics, rubbers such assilicone rubbers and so forth, backing fabrics such as those made ofnylon or polyester, electronic parts and components, and light-emittingelements. Such a cured silicone composite can be obtained by coating thepresent composition on a substrate and then thermosetting.

EXAMPLES

The curable silicone composition of the present invention will bedescribed in detail through examples and comparative examples. In theexamples, the viscosity is the value at 25° C. and parts indicates massparts.

The nature and designation of the materials used in the followingexamples for components (A)-(C) and the reaction inhibitor as a cureretarder are as indicated below. Here, Vi designates the vinyl groupwhile Me designates the methyl group.

Component A-1

a-1: a dimethylpolysiloxane endblocked by dimethylvinylsiloxy groups atboth molecular chain terminals, that has a viscosity of 500 mPa·s and avinyl group content of 0.45 mass %.

a-2: a dimethylpolysiloxane endblocked by dimethylvinylsiloxy groups atboth molecular chain terminals, that has a viscosity of 2,000 mPa·s anda vinyl group content of 0.23 mass %.

a-3: a dimethylpolysiloxane endblocked by dimethylvinylsiloxy groups atboth molecular chain terminals, that has a viscosity of 10,000 mPa·s anda vinyl group content of 0.14 mass %.

a-4: a dimethylpolysiloxane endblocked by dimethylvinylsiloxy groups atboth molecular chain terminals, that has a viscosity of 40,000 mPa·s anda vinyl group content of 0.10 mass %.

a-5: a dimethylpolysiloxane endblocked by dimethylvinylsiloxy groups atboth molecular chain terminals, that has a viscosity of 80,000 mPa·s anda vinyl group content of 0.07 mass %.

Component A-2

a-6: an organopolysiloxane given by the average unit formula(ViMe₂SiO_(1/2))_(0.04)(Me₃ SiO_(1/2))_(0.40)(SiO_(4/2))_(0.56), thathas a mass-average molecular weight of approximately 4,600, a vinylgroup content of 1.6 mass %, and a ratio of the total number of moles ofR¹ ₂R²SiO_(1/2) and R¹ ₃SiO_(1/2) units to 1 mole of the SiO_(4/2) unitof 0.79.

a-7: an organopolysiloxane given by the average unit formula(ViMe₂SiO_(1/2))_(0.06)(Me₃SiO_(1/2))_(0.38)(SiO_(4/2))_(0.56), that hasa mass-average molecular weight of approximately 4,600, a vinyl groupcontent of 2.3 mass %, and a ratio of the total number of moles of R¹₂R²SiO_(1/2) and R¹ ₃SiO_(1/2) units to 1 mole of the SiO_(4/2) unit of0.79.

a-8: an organopolysiloxane given by the average unit formula(ViMe₂SiO_(1/2))_(0.04)(Me₃SiO_(1/2))_(0.46)(SiO_(4/2))_(0.50), that hasa mass-average molecular weight of approximately 4,000, a vinyl groupcontent of 1.6 mass %, and a ratio of the total number of moles of R¹₂R²SiO_(1/2) and R¹ ₃SiO_(1/2) units to 1 mole of the SiO_(4/2) unit of1.00.

a-9: an organopolysiloxane given by the average unit formula(ViMe₂SiO_(1/2))_(0.06)(Me₃ SiO_(1/2))_(0.44)(SiO_(4/2))_(0.50), thathas a mass-average molecular weight of approximately 4,000, a vinylgroup content of 2.3 mass %, and a ratio of the total number of moles ofR¹ ₂R²SiO_(1/2) and R¹ ₃SiO_(1/2) units to 1 mole of the SiO_(4/2) unitof 1.00.

a-10: an organopolysiloxane given by the average unit formula(ViMe₂SiO_(1/2))_(0.02)(Me₃SiO_(1/2))_(0.42)(SiO_(4/2))_(0.56), that hasa mass-average molecular weight of approximately 4,600, a vinyl groupcontent of 0.75 mass %, and a ratio of the total number of moles of R¹₂R²SiO_(1/2) and R¹ ₃SiO_(1/2) units to 1 mole of the SiO_(4/2) unit of0.79.

a-11: an organopolysiloxane given by the average unit formula(ViMe₂SiO_(1/2))_(0.11)(Me₃SiO_(1/2))_(0.33)(SiO_(4/2))_(0.57), that hasa mass-average molecular weight of approximately 4,800, a vinyl groupcontent of 4.2 mass %, and a ratio of the total number of moles of R¹₂R²SiO_(1/2) and R¹ ₃SiO_(1/2) units to 1 mole of the SiO_(4/2) unit of0.77.

Component B

b-1: an organopolysiloxane given by the average unit formula(HMe₂SiO_(1/2))₈(SiO_(4/2))₄, that has a kinematic viscosity of 18 mm²/sand a silicon-bonded hydrogen atom content of approximately 0.97 mass %.

b-2: a polymethylhydrogensiloxane endblocked at both molecular chainterminals by trimethylsiloxy groups, that has a kinematic viscosity of21 mm²/s and a silicon-bonded hydrogen atom content of approximately1.57 mass %.

b-3: a dimethylsiloxane•methylhydrogensiloxane copolymer endblocked bytrimethylsiloxy groups at both molecular chain terminals, that has akinematic viscosity of 5 mm²/s and a silicon-bonded hydrogen atomcontent of approximately 0.75 mass %.

b-4: a dimethylsiloxane•methylhydrogensiloxane copolymer endblocked bytrimethylsiloxy groups at both molecular chain terminals, that has akinematic viscosity of 5 mm²/s and a silicon-bonded hydrogen atomcontent of approximately 0.45 mass %.

Component C

platinum catalyst: a 1,3-divinyltetramethyldisiloxane solution of a1,3-divinyltetramethyldisiloxane complex of platinum. The platinum metalcontent is approximately 6500 ppm.

Reaction Inhibitor as a Cure Retarder

3,5-dimethyl-1-octyn-3-ol

Examples 1 to 8 and Comparative Examples 1 to 3

The materials shown in Tables 1 and 2 were mixed to uniformity in thequantity proportions shown in Tables 1 and 2 to produce curable siliconecompositions. The resulting compositions were heated for 5 minutes at150° C. to produce the 1 mm-thick cured sheet, which was submitted tomeasurement of the tensile strength and elongation. The compositionswere also heated for 10 minutes at 150° C. to produce the 6 mm-thickcured silicone material, which was submitted to measurement of thehardness, parallel light transmittance at 25° C., and parallel lighttransmittance at 200° C. The results are given in Tables 1 and 2. TheSiH/Vi in Tables 1 and 2 indicates the ratio of the number of moles ofsilicon-bonded hydrogen in component (B) per 1 mole of the vinyl groupin components (A-1) and (A-2).

Test, Measurement, and Evaluation Methods

The properties (hardness, tensile strength, elongation, and lighttransmission) of the cured silicone material were tested, measured, orevaluated using the following methods.

(1) Hardness

A 6 mm-thick cured silicone material was fabricated by curing thecurable silicone composition by heating for 10 minutes at 150° C. Thehardness of this cured silicone material was measured using the type Adurometer specified in JIS K 6253.

(2) Tensile Strength and Elongation

A 1 mm-thick cured silicone material was fabricated by curing thecurable silicone composition by heating for 5 minutes at 150° C. Thetensile strength and elongation of this cured silicone material weremeasured according to the methods specified in JIS K 6251.

(3) Light Transmission

A 6 mm-thick cured sheet was fabricated by heating the curable siliconecomposition for 10 minutes at 150° C. The parallel light transmittanceat 25° C. and 200° C. for a 6 mm optical path length was measured on theresulting cured sheet based on JIS K 7105 using a Water Analyzer-200Nfrom Nippon Denshoku Industries Co., Ltd. Air was used as the reference.The parallel light transmittance at 200° C. is the value measured asfollows: the cured sheet is fixed in advance in a sample holder and isthen heated for 10 minutes in a 200° C. oven, after which the curedsheet is removed from the oven; measurement is then performed within 20seconds. The parallel light transmittance at 200° C. measured asdescribed in the preceding was calculated as the percentage with respectto the parallel light transmittance at 25° C., and this is reported inTables 1 and 2 as the parallel light transmittance retention rate in %.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6(A-1) (parts) a-1 a-2 55 55 55 45 a-3 20 20 a-4 47 55 a-5 (A-2) (parts)a-6 45 45 45 a-7 35 33 a-8 45 a-9 a-10 a-11 (B) (parts) b-1 5 5.2 4.6 6b-2 4.6 b-3 8.5 b-4 (C) (parts) 0.08 0.08 0.08 0.08 0.08 0.08 reactionInhibitor (parts) 0.1 0.1 0.1 0.1 0.1 0.1 SiH/Vi 1.6 2.4 1.9 1.5 1.5 2.1hardness 67 65 70 62 66 68 Tb (MPa) 12.4 7.8 10.4 7.2 8.1 10.6 Eb (%) 95130 75 150 115 90 parallel light transmittance (%) 93 93 93 93 93 93parallel light transmittance retention 100 100 100 100 100 100 rate (%)

TABLE 2 Comp. Comp. Comp. Example 7 Example 8 Example 1 Example 2Example 3 (A-1) a-1 55 (parts) a-2 50 45 a-3 20 57 a-4 a-5 65 (A-2) a-645 (parts) a-7 35 a-8 a-9 35 a-10 50 a-11 43 (B) b-1 3.5 5 10.8 (parts)b-2 3 b-3 b-4 11 (C) (parts) 0.08 0.08 0.08 0.08 0.08 reaction inhibitor(parts) 0.1 0.1 0.1 0.1 0.1 SiH/Vi 1.9 1.4 1.4 1.6 1.5 hardness 55 40 6989 74 Tb (MPa) 11.8 4.5 6.4 8.5 8.8 Eb (%) 120 300 40 43 60 parallellight transmittance (%) 93 93 93 93 93 parallel light transmittanceretention 100 100 100 98 92 rate (%)

INDUSTRIAL APPLICABILITY

The curable silicone composition of the present invention, because itforms a flexible and highly transparent cured silicone material, isuseful as an optical member or component that is permeable to light,e.g., visible light, infrared, ultraviolet, far ultraviolet, x-ray,laser, and so forth. In particular, because the cured silicone materialprovided by the cure of the curable silicone composition of the presentinvention does not undergo temperature-induced variations intransparency, this cured silicone material is well suited for use as anoptical member or component for devices involved with high energy, highoutput light. In addition, a flexible and highly transparent curedsilicone layer can be formed on the surface of any of varioussubstrates, e.g., silicone rubbers, backing fabrics made of nylon orpolyester, and so forth, by the formation of a single article with asubstrate by coating the surface of the substrate with the curablesilicone composition of the present invention and then thermosetting,and as a consequence the curable silicone composition of the presentinvention is also useful as a coating material and a surface layermaterial.

The cured silicone material of the present invention, because it isflexible and highly transparent, is useful as an optical member orcomponent that is permeable to light, e.g., visible light, infrared,ultraviolet, far ultraviolet, x-ray, laser, and so forth. The curedsilicone material of the present invention is also useful as an opticalmember or component that must be flexible, e.g., due to use in a flexedor bent condition, and is also useful as an optical member or componentfor devices involved with high energy, high output light. In addition,an article or component having a flexible and highly transparent curedsilicone layer can be made by making a composite in which the curedsilicone material of the present invention is formed into a singlearticle or body with any of various substrates, and an impact- andstress-relaxing function can also be expected from the cured siliconelayer.

1. A curable silicone composition comprising (A) 100 mass parts of analkenyl-containing organopolysiloxane comprising (A-1) adialkylpolysiloxane that has an average of at least two alkenyl groupsin each molecule and a viscosity at 25° C. of at least 1,000 mPa·s tonot more than 50,000 mPa·s, at from 50 mass % to not more than 80 mass %of component (A), and (A-2) an alkenyl-containing, resin-formorganopolysiloxane that comprises the SiO_(4/2) unit, R¹ ₂R²SiO_(1/2)unit, and R¹ ₃SiO_(1/2) unit wherein R¹ is C₁₋₁₀ alkyl and R² isalkenyl, and that contains the alkenyl group in the range from at least0.5 mass % to less than 3.5 mass %, at from 20 mass % to not more than50 mass % of component (A); (B) an organopolysiloxane that has anaverage of at least three silicon-bonded hydrogen atoms in each moleculewherein the silicon-bonded groups other than the silicon-bonded hydrogenare C₁₋₁₀ alkyl, in an amount that provides 0.8 to 2 molessilicon-bonded hydrogen in this component per 1 mole of the totalalkenyl in component (A); and (C) a hydrosilylation reaction catalyst ina catalytic quantity, and provides a highly transparent cured siliconematerial that has a hardness measured using the type A durometerspecified in JIS K 6253 is in the range from at least 30 to not morethan 80, the elongation as specified in JIS K 6251 is at least 50%, theparallel light transmittance at 25° C. measured in accordance with JIS K7105 on a 6 mm optical path length is at least 90%, and the parallellight transmittance at 200° C. is a value that is at least 99% of theparallel light transmittance at 25° C.
 2. The curable siliconecomposition according to claim 1, wherein component (B) is anorganopolysiloxane comprising (B-1) an organopolysiloxane that containsat least 0.7 mass % silicon-bonded hydrogen and that comprises theSiO_(4/2) unit and HR³ ₂SiO_(1/2) unit wherein R³ is C₁₋₁₀ alkyl, at 50to 100 mass % of component (B), and (B-2) a straight-chainorganopolysiloxane that contains at least 0.3 mass % silicon-bondedhydrogen wherein the silicon-bonded groups other than the silicon-bondedhydrogen are C₁₋₁₀ alkyl, at 0 to 50 mass % of component (B).
 3. Ahighly transparent cured silicone material provided by the thermosettingof a curable silicone composition comprising (A) 100 mass parts of analkenyl-containing organopolysiloxane comprising (A-1) adialkylpolysiloxane that has an average of at least two alkenyl groupsin each molecule and a viscosity at 25° C. of at least 1,000 mPa·s tonot more than 50,000 mPa·s, at from 50 mass % to not more than 80 mass %of component (A), and (A-2) an alkenyl-containing, resin-formorganopolysiloxane that comprises the SiO_(4/2) unit, R¹ ₂R²SiO_(1/2)unit, and R¹ ₃SiO_(1/2) unit wherein R¹ is C₁₋₁₀ alkyl and R² is alkenyland that contains the alkenyl group in the range from at least 0.5 mass% to less than 3.5 mass %, at from 20 to not more than 50 mass % ofcomponent (A); (B) an organopolysiloxane that has an average of at leastthree silicon-bonded hydrogen atoms in each molecule wherein thesilicon-bonded groups other than the silicon-bonded hydrogen are C₁₋₁₀alkyl, in an amount that provides 0.8 to 2 moles silicon-bonded hydrogenin this component per 1 mole of the total alkenyl in component (A); and(C) a hydrosilylation reaction catalyst in a catalytic quantity, andhaving a hardness measured using the type A durometer specified in JIS K6253 in the range from at least 30 to not more than 80, an elongation asspecified in JIS K 6251 of at least 50%, a parallel light transmittanceat 25° C. measured in accordance with JIS K 7105 on a 6 mm optical pathlength of at least 90%, and a value for the parallel light transmittanceat 200° C. that is at least 99% of the parallel light transmittance at25° C.
 4. The highly transparent cured silicone material according toclaim 3, wherein component (B) is an organopolysiloxane comprising (B-1)an organopolysiloxane that contains at least 0.7 mass % silicon-bondedhydrogen and that comprises the SiO_(4/2) unit and HR³ ₂SiO_(1/2) unitwherein R³ is C₁₋₁₀ alkyl, at 50 to 100 mass % of component (B), and(B-2) a straight-chain organopolysiloxane that contains at least 0.3mass % silicon-bonded hydrogen wherein the silicon-bonded groups otherthan the silicon-bonded hydrogen are C₁₋₁₀ alkyl, at 0 to 50 mass % ofcomponent (B).
 5. The highly transparent cured silicone materialaccording to claim 3, which has a hardness measured using the type Adurometer specified in JIS K 6253 in the range from at least 65 to notmore than
 75. 6. A cured silicone composite comprising a substrate thatforms a single article with a cured silicone layer that is provided bythe thermosetting of a curable silicone composition according toclaim
 1. 7. A cured silicone composite obtained by coating the curablesilicone composition according to claim 1 on a substrate and thenthermosetting the curable silicone composition.
 8. The highlytransparent cured silicone material according to claim 4, which has ahardness measured using the type A durometer specified in JIS K 6253 inthe range from at least 65 to not more than 75.